This invention relates to printers. In particular, this invention relates to thermal transfer printers for the printing of labels.
In thermal transfer printers, a thermal print head is heated to selectively transfer melted ink onto a print media such as a label. In many printers, the ink may be carried by a ribbon substrate that is fed from a supply spool, past the thermal print head, and onto a rewind spool. As the ribbon is consumed during the printing process and may need to be replaced, the ribbon cartridge is a consumable good that can be removably loaded into the printer.
It is desirable to avoid slack in the ribbon, both when the printer is in use and when the printer is between uses (i.e., sitting and ready to print, being reloaded with print media, being subjected to other maintenance, and the like). If during the printing or feeding process the ribbon has slack in it, then a crease or wrinkle may develop in the ribbon that will result in print defects. Additionally, if there is too much slack in the ribbon, the ribbon could unintentionally drag on the print media resulting in skidding.
During a printing or rewind operation, as the ribbon passes the thermal print head, static electricity can be generated. When the ribbon is removed from contact with the platen roller or print media, the static electricity between the ribbon and the platen roller or print media can cause the ribbon to unwind from the supply and rewind spools. Thus, the drive mechanism that drives the operation of the printer (and the passage of ribbon from the supply to the rewind spools) may include gears and/or tensioning mechanisms to maintain appropriate tension across the ribbon both during printing, feeding, and between print jobs.
However, in some printer configurations, when the printer is not in use, the ribbon cartridge may temporarily become disengaged from the tensioning mechanisms during reloading of print media or other maintenance. When this happens, the ribbon can unwind resulting in aforementioned problems during subsequent printing.
One method of reducing slack in the ink ribbon between printer uses (i.e., either between print jobs if tensioning mechanisms are not present in the drive mechanism or when the ribbon cartridge is disengaged from the drive mechanism) is to increase the frictional forces required to rotate the supply and rewind spools or rewind spools within the ribbon cartridge. However, the frictional force that is used to prevent unwinding of the ribbon from the spools must also be overcome during the rotation of the ribbon. Accordingly, this increases the power requirement of the motor. Providing a motor that meets the increased power requirements is undesirable, as doing so increases the cost and reduces the efficiency of the printer.
Hence, a need exists for a ribbon cartridge that maintains tension so that the ribbon does not unwind when the cartridge is not in use. Moreover, there is a need to provide a ribbon cartridge that does not require a motor with increased power requirements to overcome a frictional force to provide the ribbon tension.